Lloyd McBride, backed by most of the big guns of American labor, apparently defeated insurgent Edward Sadlowski in their bitterly contested race for presidency of the United Steelworkers of America, according to unofficial returns yesterday.

Sadlowski refused to concede defeat, claiming that votes from Tuesdays secret-ballot election in the 1.4 million member union had yet to be reported from his expected steel mill strongholds in the industrial Northeast and Midwest.

The election was being closely watched because of Saslowski's advocacy of renewed militancy iin the labor movement and the contest's possible impact on contract negotiations that are scheduled to begin Monday in the steel industry.

According to an unofficial and incomplete count by United Press International, McBride had 212,760 votes to 125,270 for Sadlowski. The Associated Press said McBride was leading Sadlowski, 296,053 to 193,192, with 3,500 the 5,300 locals reporting.

McBride's headquarters in Pittsburgh claimed McBride was holding a consistent 60-to-40 per cent margin over Sadlowski throughout the vote count Sadlowski's Chicago headquarters said its count gave Sadlowski a slight lead.

Local unions have until Feb. 18 to report their vote tallies and an official winner will not be declared until May 1.

Sadlowski, who won the presidency of the unions huge Chicago-Gary district three years ago after the government ordered a second election because of fraud in the first balloting, has been expected to challenge the outcome of Tuesdays voting if McBride won by a narrow margin.

There was no word late yesterday from Sadlowakis headquarters about whether he would contest the election, Sadlowski forces charged Tuesday that numerous irregularities occured during the voting, but a Labor that the 22 departmental advisers on hand to assist in each union district had not been informed of any serious problems.

The unions's associate counsel, Michael Gottesman, said the election had been properly conducted. "Based on what we know, this is probably the most perfect election that's been run anywhere, including public elections," he told UPI.

The votes recorded by mid-afternoon yesterday were fewer than many observers had expected. Many plants were closed because of the natural gas shortage, a factor cited by both sides in explaining the turnout.

McBride, 60, the head of the union's St. Louis district and a Steelworkers' staffer since 1940, made no statement - leaving it to retiring president I. W. Abel, his staunchest supporter, to declare victory for him.

"Why wait?" asked Abel. "He's got a victory and he ought to claim it . . . He has about a 60-to-40 margin and that's what I thought it would be all along."

During the campaign, McBride steadfastly defended Abel's 12 years at the helm of the union, the largest single member of the AFL-CIO, against charges by 38-year-old Sadlowski that the Steelworkers Union had grown flabby and complacent under Abel's leadership.

Sadlowski promised major changes in the way teh union conducts its business, including scrapping the "nostrike" agreement of 1973 under which contract issues unresolved at the bargaining table are sent to arbitration. McBride indicated he would continue most of Abel's policies.

McBride said the "no-strike" agreement ended the boom-bust cycle of steel production before contract expiration, with loss of business to foreign countries, and gave the union its best contract in history. But he said he, too, might junk the provision if this year's negotiations wind up in arbitration.

With Sadlowski attacking the whole hierarchy of organized labor and drawing support from many longtime liberal foes of AFL-CIO President George Meany and other union chief-tains, Meany dropped his customary neutrality in intra-union elections and denounced support for Saslowski by "outsiders" and "limousine liberals."

McBride also had the support of most officials of the Steelworkers, who campaigned extensively for him and were denounced for doing so by Sadlowski, who cited the activity as evidence of a lack of democracy within the union.

McBride's strongest support came from the South and West, where the union has many members form outside the basic steel industry. Basic steel, where Sadlowski concentrated his campaign, has less than one third of the union's membership and McBride was cutting heavily into Sadlowski's expected margin in some basic steel locals, including those in Pittsburgh. McBride was also running strong in Canadian locals.

McBride was counted as a likely ally of Meany's on the AFL-CIO executive council, as Abel had been. Sadlowski was seen as a rebellious foe.